1. Field of the Invention
The present invention relates to a semiconductor integrated circuit and photoelectric conversion apparatus for of converting an optical signal into an electrical signal.
2. Related Background Art
A semiconductor component such as a semiconductor integrated circuit in a photoelectric conversion apparatus has a circuit for detecting changes in ambient temperature which the apparatus uses to correct operation characteristics in accordance with changes in the temperature. For example, ambient temperature changes are detected by a method as shown in FIG. 1, in a device such as an autofocus sensor (to be referred to as an AF sensor hereinafter) which must perform high-precision processing over a large temperature change range from -20.degree. C. to +60.degree. C. FIG. 1 is a block diagram showing an autofocus-associated part of a conventional camera.
FIG. 1 schematically shows a camera unit 601. The camera unit 601 comprises a thermometer 602 arranged outside a package 605, an AF sensor IC 604 having a photoelectric conversion element 608, a thermometer circuit 603 mounted on the package 605 of the AF sensor IC 604, a lens 610 and a secondary image formation lens 606 for receiving an incident optical signal from a subject image, a microcomputer 607 for processing an image signal, and a lens control unit 609 for controlling the position of the lens 610.
The camera unit 601 receives a subject image signal via the secondary image formation lens 606, forms images A and B corresponding to right and left lenses constituting the secondary image formation lens 606 on the photoelectric conversion element 608 of the AF sensor IC, performs correlation calculation for the subject image signal by the microcomputer 607, and controls the focal point of the camera lens 610 by operation of the lens control unit 609 to calculate the distance from the lens 610 to the subject to be photographed.
The influence of changes in ambient temperature on the camera unit 601 includes changes in characteristics of the secondary image formation lens 606 upon thermal expansion/shrinkage. If the characteristics of the secondary image formation lens 606 change depending on the ambient temperature, a subject image signal to be formed into an image on the photoelectric conversion element 608 of the AF sensor IC changes in focal length and exhibits changes that depend on the temperature.
For this reason, appropriate distance measurement can be attained only when a subject image signal is sent to the microcomputer 607, an ambient temperature outside the package 605 is detected by the thermometer 602, and an image signal output from the photoelectric conversion element 608 is properly corrected by the microcomputer 607.
The influence on the AF sensor IC 604 itself by ambient changes caused by changes in temperature of the AF sensor IC 604 itself must also be considered. The magnitude of dark current noise of the photoelectric conversion element 608 inside the AF sensor IC 604 influences the precision of the AF sensor IC 604. As the temperature of the AF sensor IC 604 rises, the dark current noise increases at a predetermined ratio. The temperature of the AF sensor IC 604 is measured by the thermometer 603 on the package 605, the value is sent to the microcomputer 607 together with a subject image signal, and dark current noise correction corresponding to the temperature value is performed for the image signal, thereby measuring the distance with high precision.
In the prior art, however, since the temperature of the AF sensor IC 604 is measured on the package 605, the temperature of the AF sensor IC 604 itself cannot be accurately measured. The AF sensor IC 604 generally exhibits a temperature that is different from the temperature of the package 605 and an external temperature due to power consumption of the AF sensor IC 604. More specifically, the temperature of the AF sensor IC 604 is higher than the respective temperatures of the package 605 and like elements due to heat generated from operation of the AF sensor IC 604, and the heat dissipates via the package 605 or air. In other words, the temperature on the semiconductor substrate of the AF sensor IC 604 cannot be accurately measured by monitoring only the temperature of the package 605 and an external temperature.
Hence, to accurately correct dark current noise for the purpose of high-precision distance measurement, the temperature on the semiconductor substrate of the AF sensor IC 604 itself must be measured.
Also, the temperature of the package 605 itself is different from the external ambient temperature, and thus the thermometer 602 for ambient temperature measurement also must be employed. The thermometer 602 for ambient temperature measurement and the thermometer 603 for the AF sensor IC 604 must be separately adopted, which leads to a large number of components and high cost.